Integrated Circuit Comprising a Capacitor  with Metal Electrodes and Process for Fabricating Such a Capacitor

ABSTRACT

An integrated circuit (IC) includes at least one capacitor with metal electrodes. At least one of the electrodes ( 10  or  30 ) is formed from at least surface-silicided hemispherical grain silicon or silicon alloy. A fabrication process for obtaining such a capacitor with silicided metal electrodes is also provided.

The present invention relates to integrated circuits, more particularlyto capacitors with metal electrodes. The capacitors are used especiallyin memory cells of a memory plane.

The fabrication of capacitors is increasingly faced with problemsassociated with the high integration densities. This is because theincrease in integration density means a reduction in the area of amemory cell, while still maintaining an effective capacitance. Thus, incurrent technologies, several approaches are possible.

The most common approach is the formation of the capacitor in a trench,allowing the area of the capacitor to be increased without increasingthe area of the memory cell. The area may be further increased by afactor of about 2 by using, as lower electrodes doped polysilicon of theHSG (Hemispherical Grain) polysilicon type.

For even higher integration densities, there are several possibleapproaches that allow capacitors to be integrated into smaller andsmaller cells.

The conventional approach consists in increasing the depth of thetrench. However, this approach leads to form factors that cannot beeasily controlled. Another approach consists in reducing the thicknessof the dielectric, the risk being an increase in the leakage current.

Recent research has been carried out on the use of an insulator with ahigh dielectric constant and metal electrodes, making it possible toovercome the problems of doping three-dimensional polysilicon electrodesand to reduce the depletion capacitances associated with polysiliconelectrodes. However, the conventional metal electrodes (for example madeof TiN) are plane and their use therefore results in the factor of 2provided by the use of a HSG polysilicon being lost.

The invention aims to provide a solution to these problems.

One object of the present invention is to obtain capacitors of sizematched to integrated circuits of increasingly small size withoutreduction in their capacitance.

Another object of the present invention is to use metal electrodes thatallow the doping and depletion capacitance problems associated withthree-dimensional polysilicon electrodes to be overcome, while stillmaintaining the deposition morphology of the hemispherical grain type.

The capacitors according to the present invention also afford theadvantage of having an effective capacitance without an increase in theleakage current of the dielectric.

The present invention is therefore based on the silicidization (metalsilicide formation) of, for example, an HSG polysilicon electrode.

The present invention therefore proposes an integrated circuitcomprising at least one capacitor with metal electrodes, at least one ofthe two electrodes of the capacitor of which is formed from at leastsurface-silicided hemispherical grain silicon or silicon alloy.

This electrode may thus be either partially silicided or, preferably,entirely silicided, i.e. entirely formed from a metal silicide.

According to a second embodiment of the invention, the second metalelectrode of the capacitor is also formed from a partially or entirelysilicided layer of hemispherical grain silicon or silicon alloy.

As a variant, the second electrode of the capacitor may include a metallayer, for example a TiN layer.

The capacitor may have a planar structure or else a trench structure.

The present invention also proposes a process for fabricating acapacitor within an integrated circuit as defined above, in which theproduction of the first electrode comprises the formation of a layer ofhemispherical grain silicon or silicon alloy and the at least surfacesilicidization of the said layer.

This process makes it possible to obtain a capacitor in which the saidfirst electrode may be either partially silicided or, preferably,entirely silicided.

According to a variant of the invention, the second electrode is eitherproduced in a similar manner to the first electrode, that is to say bythe deposition of hemispherical grain polysilicon followed bysilicidization, or by depositing metal, for example TiN.

Other advantages and features of the invention will become apparent onexamining the detailed description of embodiments and methods ofimplementation, which are in no way limiting, and the appended drawings,in which:

FIG. 1 shows schematically an integrated circuit according to a firstembodiment of the present invention;

FIGS. 2 to 4 illustrate schematically the main steps of a process forobtaining the integrated circuit of FIG. 1; and

FIG. 5 shows schematically an integrated circuit according to a secondembodiment of the present invention.

FIG. 1 shows an integrated circuit IC according to the invention, whichcomprises a capacitor CP having two hemispherical-grain silicided metalelectrodes.

The integrated circuit IC includes a substrate SB in which a hollowtrench has been formed, comprising a first hemispherical-grain silicidedmetal electrode 10, covered by a dielectric 2, covered by a secondhemispherical-grain silicided metal electrode 30.

The main steps of a method of implementing the process according to theinvention, allowing the capacitor of FIG. 1 to be obtained, will now bedescribed in greater detail.

In FIG. 2, the reference SB therefore denotes a semiconductor substrate,for example made of silicon. A trench 4 is formed in the substrate SB ina conventional manner known per se.

The next step of the process is the formation of the first electrode 10.To do this, a layer 1 of hemispherical grain silicon, germanium orsilicon alloy, such as for example a silicon-germanium alloy, is formed,also in a conventional manner known per se, for example by deposition(FIG. 3). The characteristics of such a deposition are described forexample in “Fabrication and performance of selective HSG storage cellsfor 256 Mb and 1 Gb DRAM applications”, A. Banerjee, R. L. Wise, D. L.Plunton, M. Bevan, M. L. Crenshaw, S. Aoyama and M. M. Mansoori, IEEETransactions on Electron Devices, Vol. 47, No. 3, March 2000.

By way of indication, the layer 1 of hemispherical grain silicon orsilicon alloy has a thickness of 1000 to 1500 Å.

In the example described here, the silicidization, that is to say theformation of a metal silicide, is obtained from cobalt. However, thissilicidization may be obtained using other metals, such as for exampletungsten, titanium or nickel.

A nickel layer is deposited, for example by plasma vapour deposition(PVD), on the layer 1 of hemispherical grain silicon or silicon alloy.

Of course, the thickness of the nickel layer is determined according tothe phase and the thickness of the final metal silicide that it isdesired to obtain, knowing that when nickel is used, 1 Å of nickel gives2.2 Å of silicide.

Next, a first initial annealing operation is carried out, typically at atemperature below 600° C., for example at a temperature of 450° C. Thisannealing temperature depends on the nature of the material used for thesilicidization. The nickel then reacts with the silicon of the layer 1to form NiSi (FIG. 4).

The excess nickel that has not reacted may then be removed, selectivelywith respect to the silicide. This selective removal operation iscarried out, for example, by wet etching. Such wet etching isconventional and known per se, and it uses for example an H₂SO₄/H₂O₂/H₂Ochemical etchant or else an HCl/H₂O₂/H₂O chemical etchant.

What is therefore produced is a silicided metal electrode 10 with ahemispherical grain morphology on which the dielectric 2 is deposited.

The dielectric may be a conventional dielectric, with a relativedielectric constant k of 5 for example. In this case, the mainimprovement over the prior art comes from the improvement in deletioncapacitance, from the great reduction in series resistance and from thesimplification of the process, in so far as it is unnecessary to dope,by implantation, silicon or silicon alloy electrodes, this operationsometimes being particularly difficult on the sidewalls of trenches.

It is also possible to use dielectrics with a high dielectric constant,for example hafnium oxide HfO₂ (k=17), which further increases thecapacitance of the capacitor.

The dielectric 2 is covered with the second electrode. As illustrated inFIG. 1, the electrode 30 may be formed in a manner similar to the firstelectrode 10, that is to say by the deposition of HSG polysilicon, thensilicidization, preferably complete silicidization, and the removal ofthe unreacted metal.

The second electrode may also be formed for example by depositing metal(for example TiN) directly on the dielectric. In this case (FIG. 5), thecapacitor comprises a first hemispherical grain silicided metalelectrode 10 covered by a dielectric 2 covered by a second metalelectrode 31.

In the integrated circuits according to the present invention, thecapacitors are not limited to trench structures, such as those describedabove, but may also be for example of the planar type.

1-9. (canceled)
 10. An integrated circuit comprising at least one capacitor with a plurality of metal electrodes, wherein at least one electrode of the plurality of electrodes of the capacitor is formed from at least surface-silicided hemispherical grain silicon or silicon alloy.
 11. The integrated circuit according to claim 10, in which a second electrode of the capacitor is formed from at least surface-silicided hemispherical grain silicon or silicon alloy.
 12. The integrated circuit according to claim 11, in which the second electrode of the capacitor is entirely formed from a metal silicide.
 13. The integrated circuit according to claim 10, in which a second electrode of the capacitor comprises a metal layer.
 14. The integrated circuit according to claim 10, in which the at least one electrode is entirely formed from a metal silicide.
 15. The integrated circuit according to claim 14, in which a second electrode of the capacitor is formed from at least surface-silicided hemispherical grain silicon or silicon alloy.
 16. The integrated circuit according to claim 15, in which the second electrode of the capacitor is entirely formed from a metal silicide.
 17. The integrated circuit according to claim 14, in which a second electrode of the capacitor comprises a metal layer.
 18. A process for fabricating a capacitor within an integrated circuit, comprising: the production of a first electrode, of a dielectric and of a second electrode, wherein the production of the first electrode comprises the formation of a layer of hemispherical grain silicon or silicon alloy and the at least surface silicidization of the layer.
 19. The process according to claim 18, in which the production of the second electrode is similar to that of the first electrode.
 20. The process according to claim 18, in which the production of the second electrode comprises a deposition of metal.
 21. The process according to claim 18, in which the layer of hemispherical grain silicon or silicon alloy is completely silicided.
 22. The process according to claim 21, in which the production of the second electrode is similar to that of the first electrode.
 23. The process according to claim 21, in which the production of the second electrode comprises a deposition of metal.
 24. An electronic device, comprising: a plurality of integrated circuits, each of the integrated circuits comprising: at least one capacitor with a plurality of metal electrodes, wherein first and second electrodes of the plurality of electrodes of the capacitor are formed from at least surface-silicided hemispherical grain silicon or silicon alloy. 